It is often desirable to provide a molded substrate with a coating while the substrate still resides in a mold cavity after an injection molding operation has been performed. Various methods of in-mold coating have been utilized in order to improve the quality of a surface of molded products wherein the coated product is suitable for use “as is” in an end use application, or which would require less or no surface preparation treatment than heretofore utilized.
The application of in-mold coatings (IMC) to thermoplastic or thermoset materials to provide generally smooth surfaces, improve durability and other surface properties, and to reduce or eliminate substrate porosity is known. A number of in-mold coating methods have been employed for applying coatings, in compression molding methods or injection molding methods employing molding materials of thermosetting resins, such as SMC (sheet molding compound) and BMC (bulk molding compound) (e.g., U.S. Pat. Nos. 4,076,788; 4,081,578; 4,331,735; 4,366,109; 4,668,460 and 6,180,043).
During an injection molding process wherein a substrate is coated with an in-mold coating, a substrate in a melted condition is injected into a mold cavity through a mold runner in a platen between a mold cavity and an injection device. After the injection of the substrate, the injected substrate is allowed to cool and set. At this point in the process the substrate is still connected to a sprue or sprue bushing which is formed between the substrate in the mold cavity and the nozzle of the injection device, i.e. in the mold runner of the platen.
When the molded substrate has cooled sufficiently to accept an in-mold coating, the same is injected from an in-mold coating injection device onto the surface of the substrate. The in-mold coating spreads out from the point of injection and covers a predetermined surface of the substrate. As the in-mold coating is injected into the mold cavity high pressure, usually about 200, 500, or 1000 to about 5000 psi, the in-mold coating spreads out upon the surface of the molded substrate.
Typically, the in-mold coating is injected onto the same surface of the substrate on which the sprue or sprue bushing is present. Accordingly, the in-mold coating not only spreads out across the intended surface of the substrate, but also along the exterior portion of the sprue. Through the sprue, the in-mold coating can gain entrance to the injection molding device through the nozzle or other orifice thereof. The flow of in-mold coating into the injection molding device contaminates the same by its breaching action. The cross contamination between the uncured in-molding coating and melted substrate resin can produce substandard parts. It would therefore be desirable to provide an apparatus that prevents the in-mold coating from gaining entrance to and contaminating a substrate injection molding device.